1. Technical Field
This invention relates to water treatment systems and, more particularly, to a waste water treatment system for use in a rectangular clarifying tank.
2. Discussion of Related Art
The use of a water treatment system including a series of scrapers or drag flights that are carried and driven by a pair of parallel conveyor chains throughout a rectangular clarifier, i.e. a rectangular concrete settling tank, is generally known in the art. Typically, the conveyor chains are driven by sprockets within the tank. Such a system is commonly employed for removing waste solids such as grit (i.e., non-biodegradable solids such as stones, sand, or glass), sludge and scum from the waste water in the tank. This type of waste water treatment system is commonly used in rectangular clarifying tanks having widths varying from 10 feet to 22 feet. Clarifying tanks of this size are typical for many applications in the United States. An example of such a system for tanks of this size is the waste water treatment system disclosed in U.S. Pat. No. 4,645,598 to Hannum, which is hereby incorporated by reference.
Generally, in operation, the series of flights move in one direction partially above the top surface of the waste water, pushing scum into a collector for its removal. Concurrently, other flights in the series move in an opposite direction along the bottom floor of the tank with the front faces of the flights collecting and gathering settled solid waste materials such as sludge. During this process, the flights may be subjected to heavy loads, commonly referred to as sludge loads. These loads are transferred to other components of the system including, but not limited to, the conveyor chains, sprockets and drive assembly. In order to reduce the loads on the system's components, most of the working parts are made from non-metallic material which is lightweight, minimizes wear between components, and has a high immunity to the corrosive environment within the clarifying tank.
Typically, as the width of a settling tank is increased, the flight or scraper length, as well as other hardware components, must be correspondingly increased or strengthened for the removal of additional waste solids. A problem associated with simply increasing the length of the flights is that the flights will be subjected to greater sludge loads, causing excessive center deflection of the flights. Such excessive deflection creates torsional loads as well as simultaneous twisting and bending of the flights. This can cause the flights, the flight attachment links and/or other components of the system to fail. Additionally, for many typical systems, as a tank is widened, the system's drive shaft, usually spanning the width of the tank, must also be lengthened. This may cause the drive shaft to deflect or bend due to an increase in its own weight.
In an attempt to overcome problems inherent with widening a settling tank, known waste water treatment systems have increased the mass of certain portions of the flights and associated hardware. This increase in mass typically increases the flight's strength, stiffness, and resistance to deflection. However, the increased mass of the flights and associated hardware may also create excessive loads that can cause failures of other components within the system. Furthermore, the metallic materials typically used in wide settling tank applications are exposed to the corrosive and degrading nature of the waste water. This combination of factors reduces the energy efficiency and durability of such steel systems, as well as increasing maintenance costs.
To overcome the above described deficiencies, dual drive shaft systems have been developed, wherein the drive motor and gearbox are positioned at the center point between the sides of the treatment tank. Equal length shafts extend laterally from the gearbox and each include a drive sprocket on its end to drive the chains of the water treatment system.
However, many existing water treatment facilities include a drive motor positioned at the side of the tank. It should be appreciated that retrofitting an existing wide-tank water treatment system with a dual drive shaft system may not be cost effective. Moreover, the simple replacement of corroded metal parts with additional metal parts may not maximize the useful life of the system.
It is therefore desirable to provide a water treatment system for use in a rectangular clarifying tank, having significant width, which offers reduced weight and wear, high immunity to corrosion and is driven from either the left or right hand side. Additionally, the drive shaft of such a water treatment system must overcome the deficiencies of significantly long drive shafts.